Method of applying a nanocrystalline coating to a gas turbine engine component

ABSTRACT

A method of applying a nanocrystalline coating to a gas turbine engine component is described. The method comprises the steps of applying an intermediate bond coat to at least a portion of the component, and then applying the nanocrystalline coating to at least the portion of the component overtop of the intermediate bond coat. The component may include, for example, a blade of which a dovetail portion of the blade root is protected by applying the intermediate bond coat and the nanocrystalline coating thereto.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority on U.S. Provisional PatentApplication No. 61/388,364 filed Sep. 30, 2010, the entire contents ofwhich is incorporated herein by reference.

TECHNICAL FIELD

The application relates generally to gas turbine engines and, moreparticularly, to the application of a coating to a component, such as afan blade and/or other airfoil, used in a gas turbine engine.

BACKGROUND OF THE ART

Gas turbine parts such as blade and other airfoils, and particularly fanblades, experience excessive galling and wear on the dovetail pressuresurfaces. This is especially true for titanium (Ti) blades on titaniumhubs, with the Ti on Ti contact resulting in high coefficients offriction and high material transfer rates. This results in prematureblade retirement and a significant increase in maintenance costs.Additionally, surface contact points, under conditions of bladewind-milling, are subject to many cycles of low contact loads thatresult in wear. Traditionally, gas turbine manufacturers have overcomethese issues by reducing contact stress levels, using sacrificial shims,such as shown in U.S. Pat. No. 5,160,243. The problem with these shimsis that they require periodic replacement, add fan blade assemblycomplications and may result in fragment release if they fail.Accordingly, there is a need to provide improved protection to the bladedovetail surfaces.

SUMMARY

In accordance with one aspect of the present application, there isprovided a method of applying a nanocrystalline coating to a gas turbineengine component composed of a first metallic material, the methodcomprising the steps of: applying an intermediate bond coat to at leasta portion of the component; and then applying the nanocrystallinecoating to at least said portion of the component overtop of theintermediate bond coat.

There is also provided, in accordance with another aspect of the presentapplication, a method of protecting a blade of a gas turbine engine, theblade having a blade root and an airfoil extending therefrom, the methodcomprising the steps of: applying an intermediate bond coat to at leasta dovetail portion of the blade root; and then applying ananocrystalline coating to at least said dovetail portion of the bladeroot, overtop of the intermediate bond coat.

DESCRIPTION OF THE DRAWINGS

Reference is now made to the accompanying figures in which:

FIG. 1 is a schematic cross-sectional view of a gas turbine engine;

FIG. 2 is a cross-sectional view of a portion of a prior art fan bladedovetail, showing the wear and damage typical to conventional designs;

FIG. 3 is an enlarged isometric view of a root of a fan blade for use inthe engine of FIG. 1, protected by a coating as described herein,showing the fan blade and dovetail of the blade root;

FIG. 4 is a enlarged partial cross-sectional view of one example of afan blade according to FIG. 3; and

FIG. 5 is a further enlarged partial cross-sectional view of anotherexample of the fan blade according to the present disclosure.

DETAILED DESCRIPTION

FIG. 1 illustrates a gas turbine engine 10 generally comprising, inserial flow communication, a fan 12 through which ambient air ispropelled, a compressor section 14 for pressurizing the air, a combustor16 in which the compressed air is mixed with fuel and ignited forgenerating an annular stream of hot combustion gases, and a turbinesection 18 for extracting energy from the combustion gases.

Referring to FIG. 2, a typical fan blade 112 of the prior art has ablade root 120 having a dovetailed shape portion at is proximal end (andwhich root is thus often simply referred to as a “dovetail”). Thedovetail of the root 120 has a pressure side surface 122 that is subjectto wear of the type described above. The dovetail 120 of the root of theblade 112 fits within corresponding dovetail-shaped slots 124 in thedisk lug 126. While the wear areas 144 as shown in FIG. 2 may be proneto some wear and thus also experience deterioration with time duringuse, the fretting areas 146 on sloping surfaces of the dovetail 120 aremost particularly subject to fretting wear of the type noted above.

Referring to FIG. 3, the blade 12 in accordance with one embodiment ofthe present disclosure has a blade root or dovetail 20 having a wearsurface 22 thereon that is coated with a nanocrystalline metal coating(i.e. a “nano coating”) 24 thereon. The wear surface 22, or bearingsurface, may be for example a region of expected fretting wearcorresponding to the fretting areas 146 described above, and thus maycomprise an angled bearing surface which contacts a correspondingsurface within the dovetail slot of the hub. The nanocrystalline metalcoating 24 is, in at least one embodiment, applied to at least the wearsurface 22 on the pressure side of the dovetail. However, it isunderstood that the presently described nanocrystalline metal coating 24may be applied to both the pressure and suction sides of the dovetail20, either exclusively on the wear surface areas 22 or beyond (includingcovering the entire blade root, for example). The nanocrystalline metalcoating 24, such as Nanovate (a trademark of Integran Technologies)nickel (Ni) or copper (Cu), is applied to at least the pressure sidewear surface 22 of the fan blade, in order to provide a wear-resistantsurface to the blade. The nanocrystalline metal coating 24 may beapplied to the dovetail pressure side wear surface 22 only, oralternately may be applied to more of, including the entirety of, thedovetail 20, as shown in FIG. 4 for example.

The present method of applying the nanocrystalline metal coating 24 mayinclude a plating technique or other suitable method used to deposit asuitable material (example: Ni or Cu) in nanocrystalline grain structureover the desired portion of the blade dovetail. The nanocrystallinemetal coating 24 may also reduce friction coefficients between blade 12and the hub within which the root 20 thereof is received.

The thickness of the nanocrystalline metal coating 24 may range betweenabout 0.001 inch to about 0.125 inch (about 0.0254 mm to about 3.175mm), and more preferably between 0.001 inch (0.0254 mm) and 0.008 inch(0.2032 mm), but may depend on the clearance available in the particularblade and hub design. In one particular example, the nanocrystallinemetal coating 24 is about 0.005 inches (0.127 mm) in thickness. Inanother example, coating thickness varies so as to be locally thicker inregions where higher load contact stresses are present.

The nano coating is composed of a material different to that of theblade and/or hub, and therefore provides a surface of a materialdissimilar to the blade hub, which reduces galling caused inconventional assemblies by contact between similar materials used forblade root and hub. Using a coating procedure as described herein mayalso simplify the assembly relative to prior art designs which employshims and other anti-wear devices.

The nanocrystalline metal coating may be applied directly to thesubstrate, such as the titanium dovetail of the blade root, oralternately to an intermediate bond coat disposed on the substrate. Theintermediate bond coat may be first applied to the substrate to beprotected, prior to the application of the nano coating, in order toimprove bonding to the blade substrate to prevent separation of thenanocrystalline metal coating from the blade, in the event that improvedbonding between the substrate and nanocrystalline metal coating isdeemed to be required.

The nanocrystalline metal coating 24 forms an outer layer which actsstructurally to strengthen the dovetail 20 and to protect it againstwear and fretting, and to improve fatigue endurance. Due to thenanocrystalline grain size, the nano coating provides for improvedstructural properties and for improved fatigue endurance of thedovetail. The nano coating metal grain size may range between about 2 nmand 5000 nm. The nano coating may be a nickel (Ni), copper (Cu),cobalt-phosphorous (CoP) or another suitable metal or metal alloy, suchas Co, Cr, Fe, Mo, Ti, W, or Zr. The manipulation of the metal grainsize, when processed according to the methods described herein, producesthe desired mechanical properties. The nanocrystalline metal coating maybe composed of a pure or single metal, such as Ni or Co for example. Itis to be understood that the term “pure” or “single” as used herein isintended to include a metal comprising trace elements of othercomponents. As such, in a particular embodiment, the nano metal topcoat24 comprises a Nickel coating which includes trace elements such as, butnot limited to: Carbon (C)=200 parts per million (ppm), Sulphur (S)<500ppm, Cobalt (Co)=10 ppm, and Oxygen (O)=100 ppm.

The nanocrystalline metal coating 24 may be a metal selected from thegroup consisting of: Ni, Co, Al, Cu, Cr, Fe, Mo, Pt, Ti, W, and Zr, andis purposely composed of a single metal in that it exists no otherintentionally added elements. In one particular embodiment, the singlemetal is selected from the group consisting of: Co, Cu, Cr, Fe, Mo, Ni,W and Zr. The manipulation of the metal grain size produces the desiredmechanical properties for the gas turbine engine blade. In a particularembodiment, the nanocrystalline metal coating 24 is a single metal suchas nickel (Ni) or cobalt (Co), such as for example Nanovate™ nickel orcobalt (trademark of Integran Technologies Inc.) respectively, althoughother metals can alternately be used, such as for example copper (Cu) orone of the above-mentioned metals. The nanocrystalline metal coating isintended to have grain size in the nano meter scale and is purposely notalloyed for specific material properties. As noted above, it is to beunderstood that the term “single metal” is intended to include a metalperhaps comprising trace elements of other components but otherwiseunalloyed with another metal.

The nano coating may be applied, according to the present method,through a plating process in a bath, such as to apply the fine-grained(i.e. nano-scale) metallic coating to the component or article to becoated. However, any suitable plating or other coating process can beused, such as for instance the plating processes described in U.S. Pat.No. 5,352,266 issued Oct. 4, 1994; U.S. Pat. No. 5,433,797 issued Jul.18, 1995; U.S. Pat. No. 7,425,255 issued Sep. 16, 2008; U.S. Pat. No.7,387,578 issued Jun. 17, 2008; U.S. Pat. No. 7,354,354 issued Apr. 8,2008; U.S. Pat. No. 7,591,745 issued Sep. 22, 2009; U.S. Pat. No.7,387,587 B2 issued Jun. 17, 2008 and U.S. Pat. No. 7,320,832 issuedJan. 22, 2008; the entire contents of each of which is incorporatedherein by reference. Any suitable number of plating layers (includingone or multiple layers of different grain size, and/or a thicker layerhaving graded average grain size and/or graded composition within thelayer) may be provided. The nanocrystalline metals(s) used is/arevariously described in the patents incorporated by reference above.

The nanocrystalline metal coating 24 has a fine grain size, whichprovides improved structural and fatigue properties to the blade rootor, in the case of another components coated with this coating, theportion of the component to which it is applied. The nanocrystallinemetal coating is a fine-grained metal, having an average grain size atleast in the range of between 1 nm and 5000 nm. In a particularembodiment, the nanocrystalline metal coating has an average grain sizeof between about 10 nm and about 500 nm. More preferably, in anotherembodiment the nanocrystalline metal coating has an average grain sizeof between 10 nm and 50 nm, and more preferably still an average grainsize of between 10 nm and 25 nm.

In another embodiment, the above-described nano coating is applied to aconventional fan blade which has already experienced fretting and wearof the type described above—i.e. the coating is applied over the wornbut reworked and refinished surface, which may permit the re-entry intoservice of a fan blade which otherwise would have been required to beretired from service and scrapped. Hence, the application of thenanocrystalline metal coating may be used as a method of repairing wornblades, thereby structurally strengthening the fan blades and providingthem with a shield against further wear. In the case where the wornblade is titanium, as is the hub, the application of a non-titanium nanocoating, such as those described above, will prevent Ti on Ti contact,which may assist in preventing high friction and cohesive materialtransfer caused by such contact.

Many conventional fan blades are made from titanium alloy. The inventorshave found that Ti alloys bond poorly to nanocrystalline coatings andwould otherwise present reliability and durability issues if leftunaddressed. It has been found that improved results may be obtainedwhen the nanocrystalline metal coating is applied onto an intermediatebond coat, previously provided on the substrate of the blade, instead ofplating directly to the titanium alloy substrate of the blade. Thisintermediate bond coat may be made of electroless Ni plate.

Therefore, referring to FIG. 5, in one aspect the present methodinvolves the application of an intermediate bond coat 38 to the titaniumbase material of the dovetail 20, the intermediate bond coat 38 beingcomposed of an electroless nickel plate, applied using a platingtechnique to treat the titanium dovetail surface(s), prior to theapplication of the outer nanocrystalline coating 24. The electrolessnickel bond coat 38 therefore provides the titanium alloy substrate withan interface which will yield good bonding with reliable and durableplating performance with the subsequently applied nanocrystallinecoating 24 deposited overtop. The thickness of the electroless Ni platebond coat 38 may vary depending on the application. In one example, thethickness of the electroless nickel plate bond coat 38 is in the rangeof 0.00005 inch (0.00127 mm) to 0.0002 inch (0.00508) thick, but it mayoptionally be up to 0.001 inch (0.0254 mm) thick. It is to be understoodthat the intermediate bond coat may be composed of elements other thanNickel, for example elements such as Phosphorus (P), Boron (B), Thallium(TI), etc, and will depend on the material of the substrate (i.e. theblade root), as well as that of the nanocrystalline metal coating.

The presently described method of applying the intermediate bond coat 38of electroless nickel plate and the outer nanocrystalline coating 24 maybe applied during the original manufacturing of the gas turbine enginecomponent (ex: blade), or as a repair in which the coatings are added tothe dovetail of a blade which has already been in service, whether ornot the blade has yet experienced any wear. In one example, the repairis applied to a Ti fan blade which has previously had no nanocrystallinecoating but has experienced wear in the field. The repair may involve,as necessary, an initial step of preparing the worn or damaged region bystripping of any pre-existing coating and/or cleaning the surface, whichmay also include removing any uneven or damaged surfaces, and then theapplication of, first, the intermediate bond coat to the preparedregion, and then, the application of the outer nanocrystalline coatingover the intermediate bond coat. The repair may be applied to anysuitable blade composition and configuration. In another example, apreviously nanocrystalline-coated blade may be refurbished by a “stripand recoat” process similar to that described above, either as a part ofa regular engine maintenance program or as an on-demand repair, asrequired. In another example, the coating may be applied as apreventative measure to a previously uncoated blade still substantiallyundamaged by fretting, galling or windmilling wear, as the case may be.

The addition of nanocrystalline coating 24 to the Ti substrate of theblade root's dovetail 20 may improve fatigue endurance to the bladedovetail. The particular nanocrystalline coating may be selected toallow a desired heat transfer and/or anti-galling performance. Lubricityof the nano coating may be adjusted to make assembly of the dovetailinto the rotor hub slot easier, and perhaps reduce or eliminate the needfor lubricants during assembly.

In another example, a conventional nickel coating (i.e.non-nanocrystalline) may be applied to the portion of the blade whichengages the rotor hub, to provide an improved blade fixing arrangementaccording to the present method. The coating may be applied by plating,vapour deposition or any other suitable process.

The above description is meant to be exemplary only, and one skilled inthe art will recognize that changes may be made to the embodimentsdescribed without departing from the scope of the invention disclosed.For example, any suitable nanocrystalline coating and manner of applyingthe coating layer may be employed. The nanocrystalline coat may beplaced only in regions of high stress, wear, etc, or may be placed overa greater region of the dovetail and/or blade. The coating may beprovided to impede fretting or galling of the blade in use, and/or toprevent wear due to windmilling when the engine is not in use. The useof electroless nickel as an intermediate bond coat may be used to applya nanocrystalline coating to any suitable gas turbine engine component,particularly those made of titanium or titanium alloy. Still othermodifications which fall within the scope of the present invention willbe apparent to those skilled in the art, in light of a review of thisdisclosure, and such modifications are intended to fall within theappended claims.

1. A method of applying a nanocrystalline coating to a gas turbineengine component composed of a first metallic material, the methodcomprising the steps of: applying an intermediate bond coat to at leasta portion of the component; and then applying the nanocrystallinecoating to at least said portion of the component overtop of theintermediate bond coat.
 2. The method of claim 1, further comprisingselecting the intermediate bond coat of a second metallic materialdifferent from the first metallic material.
 3. The method of claim 1,wherein the step of applying the intermediate bond coat furthercomprises electroless plating the intermediate bond coat to the portionof the component.
 4. The method of claim 3, wherein the first metallicmaterial of the component is titanium or a titanium alloy, the step ofapplying the intermediate bond coat further comprising applying anelectroless nickel plating to said portion.
 5. The method of claim 1,further comprising applying the nanocrystalline metal coating byplating.
 6. The method of claim 2, wherein the first metallic materialis titanium or titanium alloy.
 7. The method of claim 2, wherein thesecond metallic material is nickel or nickel alloy.
 8. The method ofclaim 1, further comprising preparing said portion of the component forcoating, prior to applying the intermediate bond coat to said portion.9. The method of claim 8, wherein the component is substantiallyundamaged prior to performing the step of preparing, the step ofpreparing including one or more of stripping any previously appliedcoating on the component and cleaning said portion to be coated.
 10. Themethod of claim 8, wherein the method comprises repairing the componentwhich has previously been in service, the step of preparing includingincludes removing damaged regions of the component within said portionof the component.
 11. The method of claim 1, wherein the component is ablade having a root, and the portion includes a dovetail portion of theblade root.
 12. The method of claim 11, wherein the method is a methodof one of repairing and protecting a blade root from damage caused by atleast one of fretting, galling and windmilling wear.
 13. The method ofclaim 1, wherein the step of applying the intermediate bond coat furthercomprises applying the intermediate bond coat in a thickness of between0.00005 inch (0.00127 mm) and 0.001 inch (0.0254 mm) thick.
 14. Themethod of claim 1, wherein the step of applying the nanocrystallinecoating further comprises applying the nanocrystalline coating in athickness of between 0.001 inch (0.0254 mm) and 0.008 inch (0.2032 mm).15. The method of claim 14, further comprising applying thenanocrystalline coating in a thickness of about 0.005 inch (0.127 mm).16. The method of claim 1, further comprising selecting thenanocrystalline coating to be composed of a single metal.
 17. The methodof claim 16, further comprising selecting the nanocrystalline coatingfrom the group consisting of: Ni, Co, Al, Cu, Cr, Fe, Mo, Pt, Ti, W, andZr.
 18. The method of claim 1, further comprising applying thenanocrystalline coating in a non-constant thickness within said portionof the component.
 19. The method of claim 1, further comprisingselecting the nanocrystalline coating to be a metal having an averagegrain size of between 10 nm and 500 nm.
 20. The method of claim 19,further comprising selecting the nanocrystalline coating to be a metalhaving an average grain size of between 10 nm and 25 nm.
 21. A method ofprotecting a blade of a gas turbine engine, the blade having a bladeroot and an airfoil extending therefrom, the method comprising the stepsof: applying an intermediate bond coat to at least a dovetail portion ofthe blade root; and then applying a nanocrystalline coating to at leastsaid dovetail portion of the blade root, overtop of the intermediatebond coat.
 22. The method of claim 21, further comprising selecting theintermediate bond coat of a metallic material different from that of theblade.
 23. The method of claim 22, wherein the blade is composed oftitanium or titanium alloy and the intermediate bond coat is composed ofnickel or nickel alloy.
 24. The method of claim 21, wherein the step ofapplying the intermediate bond coat further comprises electrolessplating the intermediate bond coat to the dovetail portion of the bladeroot.
 25. The method of claim 21, further comprising applying thenanocrystalline metal coating by plating.
 26. The method of claim 21,further comprising applying the intermediate bond coat and thenanocrystalline coating to at least a pressure side surface of thedovetail of the blade root.
 27. The method of claim 21, wherein thedovetail portion extends axially relative to a longitudinal axis of theblade root, further comprising applying the intermediate bond coat andthe nanocrystalline coating along a substantial axial length of thedovetail portion.
 28. The method of claim 21, wherein the step ofapplying the intermediate bond coat further comprises applying theintermediate bond coat in a thickness of between 0.00005 inch (0.00127mm) and 0.001 inch (0.00254 mm) thick.
 29. The method of claim 28,wherein the step of applying the nanocrystalline coating furthercomprises applying the nanocrystalline coating in a thickness of between0.001 inch (0.0254 mm) and 0.008 inch (0.2032 mm).
 30. The method ofclaim 21, further comprising selecting the nanocrystalline coating to bea nano metal having an average grain size of between 10 nm and 500 nm.31. The method of claim 30, further comprising selecting thenanocrystalline coating to be a nano metal having an average grain sizeof between 10 nm and 25 nm.